Filter vial

ABSTRACT

A filter vial for separating biological and chemical fluids has a cylindrical sidewall with an open top and a closed bottom. A protrusion extends upwards from the middle of the bottom to form an annular recess. A tubular plunger has an open bottom end to which is fastened an annular cup having an outer sidewall sized to fit into and seal against the vial&#39;s sidewall. An inner sidewall of the annular cup holds a filter over an opening in the bottom of the plunger and forms a shaped cavity leading to that filter. The annular cup on the plunger fits into the annular recess in the vial to force fluid from the vial through the filter and into the plunger.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

BACKGROUND

Filter vials have a tubular plunger with a filter at the bottom end ofthe plunger. The plunger fits into a mating vial containing a fluid andthings suspended in the fluid. When the plunger is inserted into thevial fluid passes through the filter and into the plunger in order toseparate the fluid from particles or molecules too large to pass throughthe filter in the bottom of the plunger. The filtered fluid can beextracted from the plunger for further use.

The diameter and thickness of the filters can vary greatly from filterto filter and the thickness of the filter can vary greatly even acrossone filter. These variations make it difficult to seal the filters soall the fluid being filtered passes through the filter, and so thatfluid does not wick around the peripheral edge of the filter tocontaminate the filtered fluid in the plunger. Further, as fluid isforced through the filters the filters can bow or otherwise deform andallow fluid to bypass the filter as it enters the body of the plunger.Many current assemblies use ultrasonically welded assemblies. Even ifthe filters are ultrasonically welded to the adjacent walls of theassemblies that still leaves plasticizers that may contaminate thefluids placed in the vials during use.

Moreover, current filter vials leave a slight gap between the bottom ofthe plunger and the bottom of the vial, leaving a portion of the sampleunfiltered and unusable for future testing or processing. While thevolume of this unfiltered sample may be small in absolute terms, it mayrepresent a sufficiently large portion of the sample that its absencecan be important. There is thus a need for a filter vial that avoids theloss of fluid samples and processes more of those samples.

BRIEF SUMMARY

A filter vial for separating biological, chemical or other fluids has acylindrical sidewall with an open top and a closed bottom. Afrustoconical protrusion extends upwards from the middle of the bottomto form an annular recess in the bottom of the vial. A tubular plungerhas an open bottom end to which is fastened an annular cup having anouter sidewall that is sized to fit into and seal against the vial'ssidewall. The annular cap has an inner sidewall that holds a filter overan opening in the bottom of the plunger and forms a shaped cavityleading to that filter. The space between the cap's inner and outersidewalls mates with a tubular end of the plunger. The annular cup onthe end of the plunger fits snugly into the annular recess in the vialas the protrusion fits into the shaped recess so as to force fluid fromthe vial past the protrusion, through the filter and into the plunger.

In more detail, there is provided a filter vial and plunger assembly forfiltering fluids in which the plunger is a tubular plunger havingsidewalls defining an internal fluid cavity. The plunger has a top andbottom ends with a plunger opening in the bottom end of the plunger. Anannular cap is connected to the bottom end of the plunger. The annularcap has concentric inner and outer sidewalls with the outer sidewallconnected to an outer sidewall of the plunger and the inner sidewalldefining a shaped cavity in fluid communication with the plungeropening. The cap's outer sidewall has an outwardly extending firstsealing surface at or by its bottom. A filter is interposed between thecap's inner sidewall and the plunger opening to filter fluid passingthrough the opening. The plunger fits into a vial that has an open topand closed bottom joined by cylindrical sidewalls of sufficient diameterto form a fluid tight seal with the first sealing surface. The vial hasa protrusion extending from the center of its bottom toward the top. Theannular the bottom of the cap and the bottom of the vial havingcomplementary shapes, including complementary shapes of the protrusionand shaped cavity, to direct fluid from the vial through the shapedcavity during use. Optionally, shallow channels may be formed in thebottom of the vial and in an exterior surface of the protrusion with thechannels orientated to carry fluid toward the top of the protrusion.Preferably, but optionally, the protrusion is frustoconical.

There is also provided a filter vial apparatus having a tubular vialwith a closed bottom, an open top and a sidewall defining a cylindricalinterior with a diameter D located along a longitudinal axis of thevial. The closed bottom has a protrusion extending toward the open topand the vial bottom and protrusion define an annular recess about thevial's longitudinal axis of the vial with the protrusion at the centerof the annular recess. The apparatus also includes a tubular plungerassembly having a longitudinal axis. The plunger assembly includes aplunger with opposing top and bottom ends joined by a sidewall to definea fluid holding cavity in the plunger. The plunger's bottom end has anouter annular surface and an inner annular surface axially offset towardthe top end from the outer annular surface. The inner annular surface isgenerally orthogonal to the assembly longitudinal axis and is joined tothe first annular surface by a recess sidewall to form a recess thatencircles the assembly's longitudinal axis. The second annular surfacedefines a recess opening that is in fluid communication with the fluidholding cavity of the plunger. The assembly also has an annular cap withinner and outer concentric sidewalls defining an annular recess intowhich the outer annular surface on the bottom of the plunger is placed.The cap's outer sidewall extends over the outer surface of the bottom ofthe plunger while the cap's inner sidewall is placed adjacent thesidewall of the recess in the end of the plunger. The inner sidewall ofthe cap defines a shaped cavity configured to snugly receive theprotrusion on the vial's bottom. The shaped cavity has an upper end influid communication with the recess opening in the plunger. Further, anouter surface of the outer sidewall of the cap has a diametersufficiently larger than diameter D to form a fluid tight seal when theplunger assembly is inserted into the vial yet allowing movement of theannular cap to the bottom of the vial. The assembly also includes afilter interposed between the inner annular surface in the plunger andthe inner wall of the annular cap. Further, the annular cap on thebottom of the plunger assembly is configured to fit into the annularrecess at the bottom of the vial.

In further variations of this filter vial apparatus, the annular cap onthe bottom of the plunger conforms in size and shape to the annularrecess in the bottom of the vial and forms a snug fit with the bottomand protrusion and a snug fit or a slight interference fit with the vialsidewall. Further, the protrusion and shaped cavity may both befrustoconical with substantially the same dimensions and larger at thebottom than toward the top. Still further, shallow channels mayoptionally be formed in the bottom of the vial and the sides of theprotrusion in order to channel fluid through the channels to the filter.Also, the filter vial assembly may have a releasable end cap on the topend of the plunger, with the end cap configured to provide a fluid sealto the fluid holding cavity of the plunger. Still further, the abovefilter vial apparatus may optionally have a cap flange on the upper endof the outer sidewall of the cap with the cap flange extending outwardfrom the cap sidewall to provide the outer surface of the outer sidewallof the cap that forms the fluid tight seal with the sidewall of thevial.

The apparatus may also include an outward facing recess in the outersurface of the tubular plunger with that recess located adjacent thebottom end of the plunger and with the cap flange located in thatoutward facing recess. The plunger may have an outwardly extendingplunger flange at or adjacent to the bottom end of the outward facingrecess. The outer sidewall of the cap and outward facing recess may belocated so the outer sidewall of the cap extends over the plunger flangeand into that outward facing recess, with the outer diameter of theouter wall of the cap at the location of the flange having a diameterlarger than diameter D to form a fluid tight fit with the sidewall ofthe vial during use.

The filter vial apparatus may advantageously have the recess sidewall ina convex shape and curved toward the longitudinal axis of the plunger,with the inner sidewall of the annular cap having an outer surface isconcave and conforms to the shape of the recess sidewall to nest withthe convex surface on the recess sidewall. Further, the vial mayadvantageously be configured to hold about 10 or fewer micro liters offluid to be forced through the filter. Advantageously, the bottom of theannular cap may abut the bottom of the vial and less than about 10 microliters of fluid has passed through the filter into the fluid holdingcavity of the plunger. Also, the apparatus may include a frit or filtersupport on the upper side of the filter and abutting the filter.Preferably, the inner and outer sidewalls of the annular cap each engagea portion of the plunger to hold the annular cap onto the bottom end ofthe plunger.

In another embodiment, there is provided a filter vial apparatus havinga longitudinal axis that includes a vial, a tubular plunger and anannular cap. The vial comprises a cylindrical walled vial with a closedbottom and an open top. The vial has a centrally located protrusion onthe bottom that extends toward the top to form an annular recess at thebottom of the vial. The plunger comprises a hollow, tubular plunger thatextends into the vial. The plunger has an annular bottom with an axiallyfacing recess therein ending at an annular wall encircling and defininga recess opening in fluid communication with a cavity inside of thetubular plunger. The annular cap has inner and outer sidewalls placedover the annular bottom of the plunger with the outer sidewall on anouter sidewall of the plunger. The outer sidewall has an outer surface afirst portion of which extends outward from the longitudinal axis adistance sufficient to form a first sealing surface that forms a fluidtight seal with the cylindrical wall of the vial when the plunger isadvanced into the vial a distance sufficient to engage the first portionwith the vial's wall during use of the assembly. The inner sidewall ofthe cap fits into the axially facing recess and extends a distancesufficient to hold a filter against the annular wall of the recess andto also place the filter in fluid communication with the shaped cavityformed by the inner sidewall of the annular cap. The annular cap isconfigured to fit into the annular recess of the vial with the vial'sprotrusion snuggly fitting into the shaped cavity.

In further variations of this filter vial assembly, the first sealingsurface comprises a flange at the bottom end of the plunger forcing theouter sidewall of the annular cap outward against the vial's sidewall.Preferably, the sealing surface is located at a bottom end of theplunger and annular cap. Further, the assembly may have a second sealingsurface on the outer sidewall of the annular cap located upward of thefirst sealing surface. Advantageously the protrusion is frusto-conicalin shape and the inner wall of the cap has an inward facing surface thatis frusto-conical in shape. Further, the axial facing recess in the endof the plunger may have a sidewall that is convex in shape and the capmay have an outward facing surface on the inner sidewall that isconfigured to mate with the convex sidewall. Still further, channels inthe bottom of the vial may be placed in fluid communication withchannels in the surface of the protrusion in order to carry fluid fromthe container bottom toward the filter during use of the filter vialassembly.

There is also provided a tubular plunger assembly for filtering fluids,for use with various vials. The tubular plunger has at least an openbottom with a fluid holding cavity in the plunger. The plunger has abottom end with an inner and an outer annular surface which not onlyencircle and are orthogonal to a longitudinal axis of the plunger butare separated a distance along that by a recess sidewall that encirclesand faces the longitudinal axis to define a plunger recess in the bottomend of the plunger. The inner annular surface encircles and defines anopening to the recess which opening is in fluid communication with thefluid holding cavity of the plunger. The plunger assembly has an annularcap with a cap bottom from which extends inner and outer concentricsidewalls configured to fit over the bottom end of the plunger. Theouter sidewall fits over an outer surface of the bottom end of theplunger. The inner and outer sidewalls receive the outer annular surfacetherebetween. The inner sidewall has an outer surface abutting thesidewall of the plunger recess. The inner surface of the inner sidewalldefines a shaped cavity in fluid communication with the opening to therecess. The inner sidewall has a top end. A filter is clamped betweenthat top end of the inner sidewall and the inner annular surface.

In further variations, the tubular plunger assembly has a portion of theouter surface of the outer sidewall of the annular cap, at or by thebottom of the annular cap, extending outwardly a distance sufficient toform a first sealing surface that provides a fluid tight seal against afilter vial when the cap is inserted into the vial during use of theplunger assembly. The first sealing surface is advantageously formed bya flange on the end of the plunger which forces a portion of the cap'ssidewall outward. The plunger assembly may also include a frit orsupport interposed between the filter and the first annular surface.Further, the assembly may have a sealing surface facing along andencircling the longitudinal axis and formed on at least one of the firstand second annular surfaces. Also, the recess sidewall may have aconvexly curved shape in which case the outer surface of the innersidewall of the cap preferably has a mating concave shape. The shapedcavity is preferably frustoconical in shape. Advantageously, the tubularplunger has a sidewall that is thicker at the location of the secondannular surface. Preferably, the plunger assembly may have a removableclosure configured to releasably form a fluid tight seal at the top endof the plunger.

There is also provided a filter vial kit that includes any of the abovedescribed plunger assemblies as well as a filter vial. The filter vialmay have an open top and a closed bottom with a protrusion on the centerof the bottom. The protrusion extends toward the top a distance aboutthe same as a height of the inner sidewall of the annular cap measuredalong the longitudinal axis. The protrusion conforms in shape to theshaped cavity in the cap. The filter vial may also have an internaldiameter slightly smaller than the outer diameter of at least a portionof the outer sidewall of the cap on the bottom of the plunger to formthe fluid tight seal with the first sealing surface.

In further variations the filter vial kit may include a removable capand a volume of less than about 30 micro liters. Also, the interiorbottom of the vial and protrusion may be configured to conform to theexterior shape of the bottom of the cap and shaped recess.Advantageously, but optionally, the bottom of the filter vial may haveshallow channels formed therein which channels are in fluidcommunication with shallow channels in the surface of the protrusion.The channels are orientated to carry fluid to the top of the protrusionduring use.

Another filter vial kit is also provided in which includes a plunger, afilter, an annular cap and a vial. The plunger comprises a hollowtubular plunger having top and bottom ends with an opening at a bottomend of the plunger. The filter extends across the opening in the bottomend of the plunger. The annular cap is fastened to the bottom end of theplunger. An outer sidewall of the cap extends along an outer surface ofthe bottom end of the plunger with a portion of that outer sidewallextending outward a predetermined diameter to form a first sealingsurface. The annular cap has an inner sidewall forming a shaped cavityin fluid communication with the opening in the bottom end of theplunger. The vial has an open top and a closed bottom with the bottomhaving a central protrusion extending toward the open top of the vial.The vial also has a cylindrical sidewall that is sufficiently smaller indiameter than the predetermined diameter to form a fluid tight sealbetween the vial and annular cap. The bottom of the annular cap and theshaped recess are configured to mate with the shape of the vial's bottomand the protrusion so as to force fluid in the vial through the shapedcavity and filter.

In further variations of this filter vial kit the bottom of the vial hasshallow channels in fluid communication with shallow channels in thesurface of the protrusion so fluid is forced through the channels towardthe filter as the annular cap fits snuggly against the vial's bottom andits protrusion. Further, the inner sidewall of the cap may push thefilter against a portion of the plunger to hold the filter in place.Preferably, the shaped cavity is frustoconical and the protrusion has amating frustoconical shape with shallow channels in the surface of theprotrusion to carry fluid to the top of the protrusion.

An improved filter vial is also provided. The improved vial includes aplastic filter vial having an open top and a closed bottom connected bya cylindrical sidewall. The bottom has a protrusion extending a shortdistance along a longitudinal axis of the vial toward the top. Thefilter vial has a volume of about 30 micro liters or less and a sidewallthickness of about 0.050 inches or less. Optionally, the protrusion isfrustoconical and extends for a distance of less than about 0.2 inches.Optionally, the bottom of the vial has shallow channels therein that arein fluid communication with shallow channels in an outer surface of theprotrusion and orientated to carry fluid through the channels toward thetop of the protrusion. The channels are preferably radially orientated.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the various embodimentsdisclosed herein will be better understood with respect to the followingdescription and drawings, in which like numbers refer to like partsthroughout, and in which:

FIG. 1A is a side view of a filter vial having a protrusion or boss inits bottom;

FIG. 1B is a top view of the filter vial of FIG. 1A;

FIG. 1C is a cross-sectional view of the filter vial of FIG. 1A takenalong 1C-1C of FIG. 1B;

FIG. 2A is a side view of a plunger for use with the filter vial of FIG.1A;

FIG. 2B is a cross-sectional view of the plunger of FIG. 2A taken alongSection 2B-2B of FIG. 2A;

FIG. 2C is an enlarged portion of taken along 2C-2C of FIG. 2B;

FIG. 3A is a side view of a cup for use with the plunger of FIG. 2A;

FIG. 3B is a sectional view taken along 3B-3B of FIG. 3C;

FIG. 3C is a top view of the cup of FIG. 3A;

FIG. 4A is a side view of the cup of FIG. 3A on the plunger of FIG. 2A;

FIG. 4B is a sectional view taken along section 4B-4B of FIG. 4A;

FIG. 4C is an enlarged sectional view of the lower end of FIG. 4B;

FIG. 5A is a sectional view of the plunger of FIG. 2A with a cup of FIG.3A inserted into a vial of FIG. 1A, before filtering fluid in the vial;

FIG. 5B is a sectional view of the plunger of FIG. 5A with the plungerforcing some fluid into the plunger;

FIG. 5C is a sectional view of the plunger of FIG. 5A with the plungerabutting the bottom of the vial and all the filtered fluid in theplunger;

FIG. 6A is a partial perspective view of a further embodiment of thevial of FIGS. 1A-1B having a frusto-conical protrusion;

FIG. 6B is a bottom view of a cap having a shaped recess that mates withthe annular space and protrusion of FIG. 6A;

FIG. 7A is a partial perspective view of a further embodiment of thevial of FIGS. 1A-1B showing a protrusion with a four sidedcross-sectional shape;

FIG. 7B is a bottom view of a cap having a shaped recess that mates withthe annular space and protrusion of FIG. 7A;

FIG. 8A is a partial perspective view of a further embodiment of thevial of FIGS. 1A-1B showing a protrusion with a three-sidedcross-sectional shape;

FIG. 8B is a bottom view of a cap having a shaped recess that mates withthe annular space and protrusion of FIG. 8A;

FIG. 9A is a partial perspective view of a further embodiment of thevial of FIGS. 1A-1B showing a protrusion with a four sidedcross-sectional shape in a vial with a four sided cross-sectional shape;

FIG. 9B is a bottom view of a cap having a shaped recess that mates withthe annular space and protrusion of FIG. 9A;

FIG. 10A is a partial perspective view of a further embodiment of thevial of FIGS. 1A-1B showing a protrusion with a three-sidedcross-sectional shape;

FIG. 10B is a bottom view of a cap having a shaped recess that mateswith the annular space and protrusion of FIG. 10A;

FIG. 11 is an exploded cross-sectional view of a lower portion of aplunger, filters, filter supports or frits, and a cap.

DETAILED DESCRIPTION

Briefly described with reference to FIG. 1A-1C and 5A-5C, a tubularfilter vial 10 has a closed bottom 12 with a boss or protrusion 14located at the middle of the bottom. The protrusion 14 extends into thecavity formed cylindrical wall 16 of the vial forming an annular spacebetween the protrusion 14 and the wall 16 of the vial 10. Shallowchannels 15 are formed in the bottom 12 and sides of the protrusion 14.When a fluid sample is placed in the vial 10 the fluid surrounds theprotrusion 14. A tubular plunger 18 has a first and outer, annularbottom end 20 over which fits an annular cap 50, with the bottom ofannular cap 50 shaped to fill the annular space surrounding projection14 and fit snugly over the protrusion 14 so as to force all of the fluidin the vial 10 and annular space surrounding projection 14 through afilter 70 in the bottom of the plunger and into the inside of thetubular plunger 18 where the filtered fluid may be removed for furtheruse. The shallow channels 15 in the bottom 12 and sides of projection 14allow any residual fluid to be forced from the vial through filter 70and into the plunger 18. The annular bottom end 20 of the plunger 18 ispreferably orthogonal to the longitudinal axis 27 of the plunger, butsince the end 20 may take various shapes it need not be a flat, annularsurface. A removable end cap 23 (FIG. 5A-5C) on the upper end 22 of theplunger provides a closed container for the filtered fluid. The end cap23 is removed to access the fluid in the tubular plunger or a needle isinserted through membrane 25 to access the filtered fluid. The end cap23 may have various configurations and may attach to the end 22 of theplunger 18 various ways, including use of threads 24.

The relative directions top and bottom or upper and lower are withrespect to the parts as shown in FIGS. 1A, 2A and 3A when the drawingsare held vertically. This has the top orientated away from the earth andthe bottom toward the earth when the vial and plunger are heldvertically in a use position. The relative directions are thus those ofa person standing. Similarly, up and down or upper and lower or aboveand below refer to the relative positions of a person standing with thevial in a vertical orientation. The relative directions inner or inwardrefer to direction toward common longitudinal axis 27 of the variousparts as described later. The relative directions outer or outward referto the direction away from the common longitudinal axis 27. Further, asused herein, a snug fit means a very close fit that allows parts to fittogether when manually positioned but not an interference fit. The spacebetween snugly fitting parts may vary from zero to a few thousandths ofan inch (about 0.1 mm or less).

Referring to FIGS. 2A-2C, the tubular plunger 18 has a circularcross-section with bottom and top ends 20, 22, respectively. Threads 24may be optionally placed on the outer surface of the plunger adjacentthe top end 22 with the threads configured to mate with a threadedclosure 23 (FIG. 5A) to close off the top end of the plunger, preferablyby providing a fluid tight seal. The closure 23 may have an elastomericmembrane 25 through which a needle may be inserted to withdraw portionsof the filtered fluid from inside the plunger 18. An upper flange 26extends outward from the exterior surface of the plunger 18 toward upperend 22 of plunger 18. The upper flange 26 may various cross-sectionalshapes, with a triangular cross section being preferred. The triangularcross-section is inclined to make it easy to insert the upper flange 26into the vial 10 so the flange may seal against the interior wall 16 ofthe vial while resisting removal of the plunger from the vial. Thus, theflange 26 has one side extending outward from the exterior surface ofthe plunger 18, and preferably in radial direction from a longitudinalaxis 27 of the plunger 18, while another side is inclined so as tointersect the longitudinal axis 27 between the flange 26 and the bottomend 20 of the plunger. A vent hole 29 may be extend through the wall ofthe plunger 18, with the vent hole advantageously located close to theflange 26, but between the flange 26 and the bottom end 20. The venthole should be located well above the anticipated fluid level in theplunger 18.

The tubular fluid holding cavity in the plunger 18 preferably has acylindrical portion 28 beginning at the top end 22 with a narrowingportion 30 beginning about ¼ of the length of the plunger from thebottom end 20. The narrowing portion 30 is optional, but inclined wallsforming a truncated, conical surface are preferred. The bottom end ofthe narrowing portion 30 opens into a larger plunger recess 32 that isformed in the bottom end of the plunger 18. The plunger recess 32 isgenerally cylindrical in shape, creating a stepped configuration in thebottom portion of the plunger 18. The step may be a sharp change indiameter or a gradual one as shown in FIG. 11. The plunger's annular end20 encircles the plunger recess 32 and axis 27 so the plunger recess 32faces along axis 27. The plunger recess 32 extends from the bottomsurface 20 toward the top of the plunger for a short distance, ending atannular wall 34, which is generally orthogonal to the longitudinal axis36 of the plunger and surrounds the lower end of fluid holding cavity30. The plunger's annular end 20 may be viewed as an outer annularsurface generally aligned with or close to the outer periphery of theplunger 18, while the annular wall 34 is an inner annular surface 34located inward of and laterally offset from the first annular surface 20toward the upper end 22 of the plunger. Sidewall 36 faces and encirclesaxis 27 and join the inner edge of the annular surface 20 to the outeredge of annular surface 34. The first and outer annular surface 20 is onthe end of a tubular projection formed by the wall of the tubularplunger 16, while the second, inner annular surface 34 is offsettherefrom and defines the bottom opening to the fluid holding cavities28, 30.

The plunger recess 32 has sidewall 36 that may be parallel, inclined,curved or of other shape to help seal with mating parts that may beplaced into the plunger recess 32 as described later. A slight curve ofthe sidewall 36 is believed preferred, with the sidewall being convex sothe middle of the sidewall extends more toward the longitudinal axis 27than the ends of the sidewall 36. Thus, the plunger recess 32 has amaximum diameter of D1 at its top and bottom and a minimum diameter D2therebetween. As seen in FIGS. 2A-2C, the annular surface or wall 34 isabove plunger end 20 so the annular wall 34 may be referred to as topwall 34, of the plunger recess 32. The convex shape of the sidewall 36helps hold the annular cap 50 on the annular bottom of the plunger 18 asdescribed later.

Advantageously, but optionally, a recess sealing member 35 (FIG. 2C) isformed on the annular top wall 34 and extends along axis 27 in thedirection of the bottom of the plunger 18. A seal with a triangularcross section is preferred, and preferably the seal is at the edge ofthe juncture of the tapered fluid holding cavity 27 and the top wall 34.

An end sealing member 38 is optionally formed on the annular end surface20. The end sealing member 38 encircles the plunger recess 32 and iscentered on axis 27. A end sealing member 38 with a triangularcross-section is preferred, with the seal extending in the direction ofthe axis 27 away from the plunger's bottom end 20. Advantageously, theend sealing member 38 is formed in about the middle of the annular endsurface 20, about half way between the plunger recess 32 and the outercircumference of the plunger's end 20. As seen best in FIG. 2C, theouter surface of the plunger adjoining the end surface 20 may optionallybe cylindrical in shape for a short distance upward along axis 27. Incontrast, the inner surface of the plunger at the end surface 20 ispreferably curved as discussed above.

An annular groove 40 is preferably formed in the outer surface of theplunger 18 adjacent the bottom end 20 and encircling the end of theplunger. The groove 40 may have a flat bottom generally parallel to andconcentric with the axis 27 with perpendicular ends. The width of groove40 extends a short distance along axis 27, with the distance dependingat least in part on the configuration of a cap described later. Theouter side of the plunger 18 between the lower edge of the groove 40 andthe end 20 is generally inclined, forming a plunger flange 42 at thebottom of the plunger. Preferably, the plunger flange 42 is inclined soit intersects axis 27 below the end 20. Further, the largest diameter ofplunger flange 42 is preferably the same as that of the cylindricaldiameter of the plunger 18. As seen best in FIG. 2C, the plunger flange42 preferably ends below the plunger recess 32 as measured along theaxis 27, with the groove 40 beginning toward the top of the plungerrecess 32.

Referring to FIGS. 2B and 2C, the bottom end of the tubular plunger 18has an outer wall on which is located the plunger flange 42 radiallyopposite inner wall 36 of the plunger recess 32. As described later,each of these opposing surfaces on the lower end of the plunger 18 sealagainst a mating surface on the annular cap 50 that may be snapped intoplace over the lower end of the plunger.

Referring to FIGS. 2-4, the annular cap 50 is dimensioned so that it canbe forced over the plunger flange 42 with an interference fit while alsomating with the sidewall 36 of the plunger recess 32 to also help holdthe cap onto the end of the plunger 18. In use the annular cap 50 islocated on longitudinal axis 27. The annular cap 50 has an outer,generally cylindrical and tubular sidewall 52 and an inner generallycylindrical and tubular sidewall 54 joined at the lower ends by bottom56. The cap's outer sidewall 52 has an outwardly extending flange 58 atits free end. The inner sidewall 54 has an outward extending flange 60at its free end. The outer sidewall 52 is generally of uniform thicknessand is higher than inner wall 54, preferably having the outer wallflange 58 located beyond the end of inner wall 54.

The sidewalls 52, 54 are concentric and spaced apart a distance toreceive between them the outer annular surface 20 and the portion of theplunger sidewall on which that annular surface 20 is formed.Advantageously, the cap's sidewalls 52, 54 conform to the shape of thetubular plunger's sidewall on which the annular surface 20 is formed.Thus, the inner and outer sidewalls 52, 54 are concentric, annular wallsspaced apart a predetermined distance by bottom 56 on the top side ofthe cap 50 with a larger bottom 57 of the lower side of the cap 50. Thebottom 56 on the upward facing side of the annular cap 50 forms anannular surface extending between the facing portions of the cap'ssidewalls 52, 54, and has a radial width extending from the outside ofthe inner wall 54 to the inside of the outer wall 52. The bottom 57 onthe downward facing side of the annular cap 50 forms an annular surfacethat also extends between the sidewalls 54, 54, but it has a radialwidth extending from the inside of the inner wall 54 to the outside ofthe outer wall 52.

The inner sidewall 54 has a curved outer surface 62 (FIG. 3B) with acurvature selected to match the curvature of sidewall 36 of the plungerrecess 32 so the sidewalls 54 and 62 nest together. This mating curvedshape is believed to not only hold the cap 50 onto the end of theplunger 18 but also helps ensure the inner wall 54 pushes the filter 70against the inner annular wall 34 to form a fluid tight seal. Thus, inuse, the outer surface 62 of the inner annular sidewall 54 abuts thesidewall 36 of plunger recess 32 in the end of the plunger 18, with thesidewalls 54, 36 forming a fluid tight seal.

The inner sidewall 54 has an inner surface 64 (FIG. 3B) shaped to fitover protrusion 14 (FIG. 1C) with a snug fit and optionally with aslight interference fit. Preferably, but optionally, the inner surface54 is a segment of a conical surface (frustoconical), with the surfacetapered to intersect longitudinal axis 27 above the ends of thesidewalls 54, 58. Thus, the cap's inner sidewall 54 forms a shapedcavity 66 centered about longitudinal axis 27. Advantageously, the cap'sinner sidewall 54 is inclined outward toward the bottom end of theannular cap 50, and preferably has that outward inclination along theentire length on the inside of the inner sidewall 54. Advantageously,the top 68 (FIG. 3B) of the cap's inner sidewall 54 forms a circularopening that is the same as the circular opening on the inside of innerannular wall 34 of the plunger recess 32 (FIG. 4C), to form an hourglassshape in cross-section, with the filter 70 at the narrow point of thehourglass. The upper end of the inner sidewall 54 forms an annularsurface 68 which abuts the filter 70 during use and pushes the filteragainst the inner annular surface 34 of the plunger 18.

Referring to FIGS. 2-4 and 11 and especially to FIGS. 2C, 3B and 4A-4Cthe formation of plunger assembly 69 is described in which the cap 50 isplaced on the plunger 18 to hold a filter 70 and optionally a frit orsupport 72 in place. The outer wall 52 has an inner surface with adiameter that is slightly smaller than the largest diameter of theplunger flange 42 of the plunger 18 so that an interference fit iscreated when the upper end of the annular cap 50 is forced over thelower end of the plunger 18. The cap's outer sidewall 52 is flexibleenough so that it bulges slightly outward at the location of the plungerflange 42, with the upper portion of sidewall 52 fitting into groove 40in the lower end of the plunger. The plunger flange 42 advantageouslyforms a fluid tight seal with the outer wall 52 of the annular cap 50.During use, the plunger flange 42 is preferably configured so that ithas a taper that makes it easier to fit the plunger flange 42 into thecap 50, but hinders removal of the cap from the flange after the partsare engaged.

As the plunger flange 42 seals against the outer wall 52 of the annularcap 50, the outer surface of the inner wall 54 of the annular cap sealsagainst the inward facing surface 36, or sidewall 36, of the plungerrecess 32 in the end of the tubular plunger 18. The flange or rib 58 onthe outer wall 52 of the cap 50 fits into the groove 40 on the plunger.The flange 58 may abut the upper side of the groove 40 in order to limitrelative motion of the outer sidewall 52. The flange 58 within thegroove 40 also provides resistance to removing the cap 50 from theplunger.

Likewise, the inner wall 54 both seals against the plunger 18 andhinders removal of the cap from the plunger. In the depicted embodimentthe sidewall 36 is convex toward the axis 27 and the outer surface ofsidewall 54 is curved (concave) to mate with convex sidewall 36. Thecap's inner sidewall 54 engages the plunger sidewall 36 to form a fluidtight seal and help hold the parts together. Other mating shapes couldbe used on the surface 36 and sidewall 54.

Preferably, the bottom 56 of the annular cap 50 is sized to accept theannular bottom 20 of the plunger 18, with the optional end sealingmember 38 abutting the bottom 56 (FIG. 4 c). Thus, the annular cap 50may be forced over the plunger flange 42 on the bottom end of theplunger 18, with the plunger flange 42 forming a snap lock to hold thecap in place, and the cap forming fluid tight seal with the bottom endof the plunger. Further, the annular cap 50 has an outer wall 52 thatseals against the outer surface of the plunger 18 at the bottom end ofthe plunger and advantageously hinders removal of the cap from theplunger. The annular cap 50 further has an inner wall that seals againstthe inner surface of the plunger 18 (sidewall 36) at the bottom end ofthe plunger and advantageously also hinders removal of the cap from theplunger. The annular cap 50 defines a fluid passage 66 which the cap 50places in fluid communication with the opening in the lower end oftapered fluid holding cavity 30.

Advantageously, the cap's inner wall 54 has a height h corresponding tothat of protrusion 14 (FIG. 1C) which height also preferably places theupper, annular end 68 (FIG. 3B) of that sidewall 54 immediately adjacentor abutting the top wall 34 of the plunger recess 32 and filter 70 butsuch that the bottom of the tapered fluid holding cavity 30 (FIG. 4B,4C) is aligned along axis 27 with the top of shaped cavity 66. Referringto FIGS. 4B-4C, the cap's inner sidewall 54 preferably leaves a slightgap between its upper end 68 and the top wall 34 of plunger recess 32. Afilter 70 and preferably but optionally a frit or support 72 are placedin that slight gap. The filter 70 is preferably below the frit orsupport 72 so that the frit or support 72 can support the filter againstupward fluid pressure from shaped cavity 66 into fluid holding cavity30. The outer periphery of filter 70 and frit or support 72 are clampedbetween the top wall 34 of the plunger recess 32 (FIG. 2C) and the topend 68 of the inner sidewall 54. There may be any number of filters 70or frits/supports 72, in various arrangements as partially illustratedin FIG. 11. The number and arrangement of filters 70 and frits orsupports 72 will vary with the specific application and design, as willthe shape of the filters and frits or supports. In particular, one ormore filters 70 may be on the upstream or downstream side of the frit orsupport 27, and the filters may be separate from or attached to the fritor support 72. Further, because the sidewall 36 of recess 34 is curved,the filter 70 and frit or support 72 may have a diameter large enough tobe placed adjacent the larger diameter portion of the sidewall 36 (FIG.2C) that is immediately adjacent the top wall 34 (FIG. 2C), with thecurvature of the sidewall temporarily holding the filter and/or frit orsupport in place. Moreover, the diameter of the seal 70 and any frit orsupport 72 are preferably large enough to extend past sealing member 35on the top wall 34 of cavity 32 in the end of the plunger 18. Thesealing member 35 helps provide a fluid tight seal between the top wall34 and end 68 of the cap's inner wall 54 and any intervening filter orfrit/support.

The filter 70 is preferably, but optionally made of Teflon, nylon, glassfiber or other filter materials such as PVDF (polyvinyldifloride) or PES(polyethersulphone), etc. The support or frit 72 is preferably made ofthe same plastic as the plunger 18 or cap 50, but porous or otherwiseallowing fluid passage. Frit 72 may be made of Teflon or glass mesh.Both the filter 70 and fit or support 72 may be very thin when thevolume to be passed there through is measured in micro liters. Thespacing between the inner sidewall 54 of the cap 50 and top wall 34 ofthe recess in the plunger 18 are selected to hold these thin parts(filter and/or frit/support) in place without breaking the support 72and with enough force so fluid may be forced through the filter 70during use. The inner wall 54 and plunger 18 thus clamp the filter 70and/or frit or support 70 in position. If the filter is strong enough byitself to safely withstand fluid forced through it during use, thefrit/support 72 may be omitted. If not, then a fit or support 72 ofsuitable thickness and strength is provided. Because the plunger 18and/or a thicker plunger sidewall may be made of stiffer material thanthe annular cap 50, or because the shape of the lower end of the plunger18 makes it much stiffer along the axis 27 at the location of the cap50, it is believed possible to force the cap 50 and its inner wall 54sufficiently tight against the plunger 18 so as to clamp the filter 70between the inner wall 54 and top wall 34 that a support or frit 72 maynot be needed for all applications. Thus, the plunger assembly 69advantageously has both a filter 70 and frit or support 72 interposedbetween the annular cap 50 and the lower end of the plunger 18, but mayomit the fit or support 72.

As reflected in FIG. 4C, when the annular cap 50 is snap-fit onto thebottom end of the tubular plunger 18 to form the plunger assembly 69,the facing portions of curved sidewall 36 and inner sidewall 54 on thesidewall 36 and inner wall are preferably not in an interference fit.Further, the bottom end of the plunger 18 adjacent the bottom end oftapered fluid holding cavity 30 is thicker and thus stiffer than theupper portion of the plunger, thus providing a stiffened plunger end.The tapered fluid holding cavity 30 in the bottom end of the plunger 18has an opening that is aligned with the opening of shaped cavity 66 inthe annular cap 50. The diameter of the tapered fluid holding cavity 30preferably narrows along the longitudinal axis 27 as you move toward theshaped cavity 66 and the cavity 66 narrows toward the fluid holdingcavity 30 along the longitudinal axis as you move toward the fluidholding cavity 30, to form a generally hourglass shape, or to form aventuri shape. As shown in FIGS. 4A and 4B, the resulting plungerassembly 69 has a lower portion of a generally uniform outer diameterexcept for an outward extending protrusion adjacent the location offlange 58 at the end of cap 50 and/or plunger flange 42.

Referring to FIGS. 1C, 4B, 4C, and 5A, 5B and 5C, the plunger assemblyof FIG. 4 is placed into the open end 80 of vial 10. That open end 80advantageously has an inwardly and downwardly tapered opening to make iteasier to align and insert the bottom end of plunger assembly 69 intothe vial 10. Advantageously, but optionally, a rib 82 extends around thetop end of the vial to provide extra strength around the opening to thevial. The inner diameter of the sidewall 16 of the vial 10 has adiameter corresponding to the diameter of the bottom end of the annularcap 50 or slightly larger. But the inner diameter of the vial's sidewall16 is smaller than the diameter of the plunger assembly at the locationof the cap flange 58, and preferably at the diameter of the plungerflange 42 so as to create an interference fit at both locations when theplunger assembly 69. An interference fit of a few thousandths of an inch(about 0.1 mm or less) at the location of rib 58 and plunger flange 42within the vial 10 is believed suitable when the volume of fluid beingfiltered is measured in micro liters, but the amount of intereferencefit will vary with the materials selected.

Preferably, as the cap's outer sidewall 54 passes over flange 42 (FIGS.2A, 4A) the sidewall 54 bulges slightly outward a distance sufficient toform a primary seal between the annular cup 50 and the sidewall 16 ofthe vial 10. This primary seal provides a sufficient interference fit sothat fluid in the vial 10 does not pass this primary seal. A secondaryseal is provided by the interference fit formed by the rib 58 pressingagainst the inside of the vial's sidewall 16. Advantageously no fluidenters the area between the seals provided by plunger flange 42 and thecap's rib 58 on the outer sidewall 52. Since the fluid in the vial 10does not pass the fluid seal formed by the plunger flange 42 forcing thecap sidewall 52 outward to abut the inside of the vial's sidewall 16,fluid flows into the plunger 18 as the plunger and vial bottom 12 movetoward each other. The inner surface of vial sidewall 16 is preferablyslightly tapered to allow the parts to be more easily molded and toincrease the slight interference fit between the primary and secondaryseals provided by plunger flange 42 and outwardly extending rib 58 onthe annular cap 50. A slight taper of a few thousandths of an inch orless (about 0.1 mm or less) over the height of the vial is believedsuitable when the vial is about an inch (25 mm) high.

As the plunger assembly 69 moves toward the vial's bottom 12, the shapedcavity 66 in the annular cap 50 on the end of the plunger assembly 69 isaligned with and fits over the protrusion 14 at the vial bottom 12. Theprotrusion is preferably frusto-conical in shape but otherconfigurations may be used as shown in FIGS. 6-10 and discussed later.More importantly, the shape of the protrusion 14 is shaped to fit snuglyinto the shaped cavity 66. As the plunger assembly 69 is advanced alongaxis 27 toward the vial's bottom vial 12, the seal between the plungerassembly 69 and the vial sidewall 16 forces fluid toward the vial bottom12, through the shaped cavity 66 and the filter 70 and into the body ofthe plunger 18 represented by cavies 30, 28.

Referring further to FIG. 5B and FIG. 1C, as the bottom end of theplunger assembly 69 reaches and passes the top of the protrusion 14, theremaining fluid in the vial 10 is forced between the inclined sides ofthe protrusion 14 and the mating sides of shaped cavity 66 to force thefluid through the filter 70 and into the fluid holding cavity 30 and/or28. Referring further to FIG. 5C and FIG. 1C, when the bottom end ofplunger assembly 69 abuts the bottom 12 of the vial 10, almost all orall of the fluid along the vial's bottom 12 and protrusion 14 is forcedthrough the filter 70 and the top of the protrusion 14 preferably abutsthe filter 70, and ideally may slightly push against the filter 70 butnot break the filter and any frit or support 72. The channels 15 in thevial's bottom 12 and sides of protrusion 14 form fluid passageways toallow fluid in the vial to pass through filter 70. As the cap's outersidewall 52 seals against the vial sidewall 16 fluid is forced towardvial bottom 12 and as the cap's bottom 57 is pushed against the vial'sbottom 12 any trapped fluid is forced into the shallow channels 15 andforced through filter 70. Indeed, if the plunger assembly 69 is forcedagainst the vial bottom 12, the bottom 57 of annular cap 50 may beforced slightly into the shallow channels 15 and provide sufficientpressure to move any trapped fluid through the channels 15 and throughthe filter 70 as the top of the protrusion 14 abuts the filter. Channelsa few thousandths of an inch or less deep (about 0.1 mm or less) andabout the same in width are believed suitable. Four to eight channelsare believed suitable but the number and size of the channels 15 willvary with the particular design and size of the vial 10.

The cap 50 on the bottom end of plunger 18 thus forms an annular maleprotrusion formed by the outer surface of the cap's outer sidewalls 52and the inner surface of the cap's inner sidewall 54, with the shapedrecess 66 at the center of the male protrusion. The annular maleprotrusion is effectively formed by the bottom 57 and sidewalls 52, 54of the cap 50 that is fastened to the bottom end of the plunger 18. Acomplimentary shaped annular, female recess is formed by the vial'ssidewall 16, bottom 12 and protrusion 14. Likewise the male protrusion14 in the vial is shaped to mate with the female recess of the shapedcavity 66. The male protrusions and female recesses fit together tosqueeze any fluid between them toward the center protrusion 14 and intothe body of the tubular plunger and fluid holding cavity 30 and/or 28.The mating annular shapes of the end of the plunger (provided by theshape of the bottom portion of the annular cap) on the one hand and theannular recess of the vial on the other hand, provide means forminimizing the dead volume at the bottom of the vial, with the shapedprotrusion 14 and correspondingly shaped recess 66 directing the fluidthrough filter 70 and into the body of plunger 18 and with the channels15 in the vial bottom 12 and sides of the protrusion 14 allowing anysmall trapped portions of the fluid to be forced through the channelsand through filter 70 abutting protrusion 14. While the annular space iscircular in the depicted embodiment of FIGS. 1-5, the annular space neednot be cylindrically based as the mating shape of the protrusion 14 andrecess 66 may be non-circular, and the shape of the vial's sidewall 16and plunger 18 need not be cylindrical but may be any tubular shape,including shapes with continuous curves such as circular or oval, orshapes with straight sides including triangular, quadrilateral ormultilateral. Thus, as used herein the use of “annular” is not limitedto shapes or volumes having concentric circles, but includes shapesother than circles. For example, FIGS. 7-8 show a protrusion 14 with across-section shape of a triangle and quadrilateral, respectively, butin a cylindrical vial 10, while FIGS. 9-10 show protrusions with threeand four sides, respectively, in vials 10 having the same number ofsides. The space surrounding the protrusion 14 and enclosed by the vialsidewall 16 is still “annular” as used herein. As used herein, the spaceis annular when the vial sidewall 16 is non-circular in cross section asin FIGS. 9-10, and had, for example cross-sectional shapes that werecontinuous curves such as circles or ovals, or shapes having straightsides including three, four or more sides joined by corners that werepreferably, but optionally rounded. As seen in FIGS. 7-10, the shapedcavity 66 in cap 50 conforms to the shape of the protrusion to form asnug fit. In multi-sided configurations of the protrusion 14 the cornersare preferably rounded but may be sharp as shown, with the corners ofthe shaped cavity 66 preferably conforming to the corners of theprotrusion to form a snug fit.

Further, the outwardly inclined surfaces of the vial's male protrusion14 and of the cap's inner sidewall 54 cooperate with plunger 18 toprovide means for deforming the outer sidewall 52 and bottom 57 of thecap 50 against the vial's sidewall 16 and bottom 12, respectively, toreduce the fluid retained between the plunger assembly 69 and vial'ssidewall 16 and bottom 12 as the plunger is moved against the bottom 12of the vial. The primary seal between the vial's sidewall and theplunger flange 42 and bulging cap sidewall 52 is an interference fitwhich forces fluid in the vial 10 downward toward the vial bottom 12 asthe plunger 18 moves the primary seal toward the vial's bottom 12 wherethe trapped fluid is directed by the mating surfaces of annular cap 50,channels 15 and protrusion 14 to pass through the filter 70. As thebottom 57 and inner sidewall 54 of the annular cap 50 approach a snuglyfit against the vial's bottom 12 and protrusion 14, any remaining fluidis forced through channels 15, through filter 70 and into the plungercavity or cavities 28, 20.

While preferred, it is not believed necessary for both the protrusion 14and inner sidewall 54 to both have lower portions inclined outward fromaxis 27. But is preferred as it is believed that the outward inclinationof the protrusion 14 mating sidewall 54 of the annular cap 50 helpdeform the cap's outer sidewall 52 outward against the vial's sidewall16 and toward the vial's corner where the vial's sidewall 16 joinsbottom 12 so as to squeeze any remaining fluid into and through theshallow channels 15 through the filter 17.

The downward movement of the plunger 18 and cap 50 are limited by thecap bottom 57 abutting the vial bottom 12. At about the time the bottom57 of the cap on the plunger assembly 69 reaches the top of theprotrusion 14, or shortly before, the upper flange 26 on the plungerabuts the wall 16 and advantageously forms a further fluid tight seal.The upper flange 26 is located on the plunger 18 to engage the sidewall16 when the cap's bottom 57 on the plunger assembly 69 is adjacent thetop of protrusion 14. Likewise, the diameter of flange 26 is selectedrelative to the diameter of the wall 16 to form a suitable seal. Theengagement of upper flange with the vial sidewall 16 helps stabilize theplunger 18 as it is pushed into the vial, and helps align the bottom ofcap 57 with the vial bottom 12. An optional fill line 84 may be providedon the outer surface of the filter vial 10 to indicate a preferred fluidlevel for use with the vial. As desired, printed indicia 86, such as“fill line” may also be provided adjacent the fill line 84 to moreclearly identify the purpose of the line.

There is thus advantageously provided an annular cap 50 with inner andouter sidewalls 54, 52, respectively. The inner sidewall is preferablyoutwardly inclined or curved at the bottom of the sidewall. The annularcap 50 is preferably molded of an elastomeric material, and preferablyone that is incompressible. The annular cap 50 and inclined sidescooperate with protrusion 14 having an outwardly inclined wall at thebottom 12 of the vial 10, so as to force the outer wall 52 of theannular cap 50 toward the vial's sidewall 16 in order to force fluidaway from the sidewall and toward the bottom 12 of the vial where it isforced upward past the cap's inner sidewall 54, through the throughfilter 17 and into cavities 30 and/or 28 in the tubular plunger 18.

The plunger 18, annular cap 50 and vial 10 are preferably molded of asuitable plastic, preferably one that does not contaminate samplesplaced in the vial 10. The fluid samples are commonly chemical orbiological samples, but any fluid to be separated may be used. The vialand annular cap are preferably made of polyolefin, preferablypolypropylene, or other suitable polymer that does not react with theintended fluid to be separated using the vial 10. The plunger 18 isadvantageously made of a stiffer material, or thicker material than thecap 50 so it is sufficiently stiff to allow plunger 18 to be forced intothe cap 50 and to further deform the cap 50 into and against the vial'sbottom 12 and protrusion 14. That stiffness may be achieved by using adifferent material, or by configuring the plunger 18 to be stiffer, asby a thicker sidewall at the location during use of the sealing surfacesformed by flange 40 and rib 58.

There is also advantageously provided a method for filtering fluidsamples using a filter vial. The annular cap 50 is fit onto the end ofthe tubular plunger 18, with the cap's inner wall 54 placing the cavitydefined by that inner wall in fluid communication with the internalfluid holding cavity 28, 30 of the tubular plunger 18, and with thecap's inner wall also clamping the filter 70 against the top wall 34 ofthe plunger recess 32 in the end of the plunger 18. Advantageously thestep of placing the annular cap 50 on the end of the plunger 18 alsoincludes snap-fitting the cap over a barb or plunger flange 42 on theplunger to releasably fasten the cap to the plunger. The cap 50 forms anannular shaped protrusion on the end of the plunger holding the filtercovering the shaped cavity 66 formed by the inner sidewall 54 of theannular cap. Fluid is placed in vial 10, preferably up to the levelindicated by fill line 84, before or after the cap is placed on theplunger. The bottom of the plunger and cap are then inserted into theopening 80 of the vial and pushed toward the vial bottom 12 (or viceversa), with the bulge in outer cap wall 52 formed by plunger flange 42and/or the flange 58 on the cap 50 forming a fluid tight seal with thevial wall 16. Further relative movement of the plunger assembly 69toward the vial bottom 12 forces fluid through the shaped cavity 66 inthe annular cap 50, through filter 70 and into one or both internalcavities 28, 30 of the plunger. As the bottom end 57 of the plungerassembly 69 passes the protrusion 14, the annular end of the plungerassembly enters the annular bottom of the vial 10, with the matingshapes forcing fluid upward, past central protrusion 14, through theshaped cavity 66 and filter 70 and into the cavities 28 and/or 30 in thebody of the tubular plunger 18. The process may include placing a cap onthe upper end of the tubular plunger 18, preferably before affixing theannular cap to the bottom end of the plunger, and preferably beforeforcing fluid into either fluid holding cavity 28, 30 inside the plunger18.

The above apparatus and process are believed to force much more of thefluid sample through the filter 70 than prior filter vials. When smallfluid samples are used the improvement in the volume filtered isespecially noticeable. The filter vial 10 is believed especiallysuitable for fluid samples of about 10 μl, but may be used with largersamples where maximum sample recovery is important. Thus, the fill line84 is preferably located to contain about 10 micro liters between thefill line and the bottom 12. The method and apparatus are even moreuseful when the fluid samples are smaller than 10 μl, such as samples of1 through ten micro liters in one micro-liter increments. While theworking volume of the vial 10 is preferably about 10 micro liters orsmaller, the total volume of the vial may be about 30 micro liters orslightly larger. A vial 10 having an internal diameter of about onethird inch (8 mm) in diameter and about one inch (25 mm) long with wallsabout 40 thousandths of an inch (1 mm) thick is believed suitable. Whilethe plunger and vial are especially suited for small fluid samples, thedesign is applicable to larger parts. The cost of the fluid filtered bythe vial, plunger, annular cap and filter can be significant, and evensmall volumes of fluid may be important and costly. Thus, thisdisclosure is not limited to fluid samples measured in a few microliters but may include much larger samples of milliliter volumes andeven larger.

The plunger 18 is preferably made of an equally strong or stronger andharder material than the annular cap 50. The thickened end of theplunger 18 formed by the tapered internal fluid holding cavity 30 allowsa stronger end. But the fluid holding cavity 30 need not be tapered andcould be the same diameter as fluid holding cavity 28 in the upperportion of the plunger. The fluid holding cavity 30 could also have astepped interior shape with one or more steps that reduce the diameterof the cavity 28 as it approaches end 20. Regardless of the shape of thecavity 28, it is preferred that the cavity result in thickened wall ofthe plunger 18 at the groove 40 and flange 58 which at least partiallyfits into that groove. A thickened plunger wall provides a strongsupport to urge the seals formed by flanges 58, 42 into sealing contactwith the cap 50 and sidewall 16 of vial 10. Preferably the plunger 16 isof the same material as the annular cap 50, but the cap's outer sidewall52 is made thin enough to flexibly extend over plunger flange 42 andinto groove 40.

The above description is given by way of example, and not limitation.Given the above disclosure, one skilled in the art could devisevariations that are within the scope and spirit of the inventiondisclosed herein, including various ways of shaping the flanges 45, 58and protrusion 14 and shaped cavity 66. For example, as shown in FIGS.______, the protrusion 14 and shaped cavity 66 may have various matingconfigurations other than the preferred frusto-conical shape shown inFIGS. 1, 5 and ______, including, but not limited to oval shapes andmultisided configurations. FIGS. ______ show protrusions 14 andcorrespondingly shaped cavities 66 having three sides and four sidesrespectively. If flat sided protrusions 14 are used the corners of theprotrusion and mating cavity 66 in the cap are preferably, butoptionally rounded as the curved corners are believed to make the partseasier to make. Further, the various features of the embodimentsdisclosed herein can be used alone, or in varying combinations with eachother and are not intended to be limited to the specific combinationdescribed herein. Thus, the scope of the claims is not to be limited bythe illustrated embodiments.

1-44. (canceled)
 45. A tubular plunger assembly for filtering liquids,comprising: a tubular plunger assembly having a cylindrical bodyextending along a longitudinal axis to enclose a liquid cavity in theplunger, the plunger assembly having a bottom end with a shaped cavityin liquid communication with the liquid cavity, the bottom endconfigured to block the passage of liquid except through the shapedcavity, the plunger assembly having at least one piston seal encirclingthe longitudinal axis and an outer circumference of the plungerassembly, the piston seal located adjacent the bottom end of the pistonassembly; a filter connected to the plunger assembly and interposedbetween the shaped cavity and the liquid cavity in the plunger andconnected to the plunger assembly to filter all liquid passing throughthe shaped cavity and into the liquid cavity of the plunger. wherein theplunger has a cross section orthogonal to the longitudinal axis that iscircular.
 46. The tubular plunger assembly for filtering liquids ofclaim 45, wherein the shaped cavity is frusto-conical in shape andcentered on the longitudinal axis.
 47. The tubular plunger assembly forfiltering liquids of claim 45, wherein the filter is connected to thepiston assembly by a cap having sidewalls parallel to the longitudinalaxis and encircling the bottom end of the piston assembly, the caphaving a bottom connected to the shaped cavity.
 48. The tubular plungerassembly for filtering liquids of claim 45, wherein the plunger assemblyis made of plastic.
 49. The tubular plunger assembly for filteringliquids of claim 45, further comprising a filter support connected tothe tubular piston assembly and located on an upper side of the filterand abutting the filter to restrain movement of the filter past thefilter support during use.
 50. The tubular plunger assembly forfiltering liquids of claim 45, wherein the at least one seal comprisestwo seals.
 51. A filter vial kit, comprising: the tubular plungerassembly of claim 45; and a filter vial having an open top defined by avial sidewall encircling the longitudinal axis during use, the vialhaving a closed bottom connected to the sidewall, the closed bottom ofthe vial having a protrusion that extends toward the open top apredetermined distance, the protrusion configured to fit snugly withinthe shaped cavity during use, the at least one piston seal configured toform a liquid tight seal against an inner surface of the vial'ssidewall.
 52. The filter vial kit of claim 51, wherein the protrusion isconfigured to fit snugly into the shaped cavity when a distal end of thetubular plunger assembly abuts the bottom of the vial.
 53. The filtervial kit of claim 51, wherein the shaped cavity is frusto conical andcentered on the longitudinal axis and wherein the protrusion isfrusto-conical and centered on the longitudinal axis.
 54. The filtervial kit of claim 51, wherein the shaped cavity has sides that areinclined toward the filter and toward the longitudinal axis.
 55. Thefilter vial kit of claim 51, wherein about the same as a height of theinner sidewall of the annular cap measured along the longitudinal axis,56. The filter vial kit of claim 51, wherein the vial bottom has groovesdirecting the flow of liquid toward the protrusion.
 57. The filter vialkit of claim 51, wherein the protrusion has grooves directing the flowof liquid toward the open end of the vial.
 58. The filter vial kit ofclaim 51, further comprising a vial cap configured to cover the open endof the vial.
 59. The filter vial kit of claim 51, wherein the at leastone seal on the piston assembly comprises two seals, and furthercomprising a third seal encircling the tubular piston assembly andlocated to sealingly engage the vial before the protrusion fits into theshaped cavity during use of the kit.
 60. A filter vial kit, comprising:the tubular plunger assembly of claim 51; and: a filter vial having anopen top defined by a vial sidewall encircling the longitudinal axisduring use, the vial having a closed bottom connected to the sidewall,the closed bottom of the vial having a protrusion that extends towardthe open top a predetermined distance, the protrusion configured to fitsnugly within the shaped cavity during use, the at least one piston sealsealing against an inner surface of the vial's sidewall.
 61. The filtervial kit of claim 60, wherein the protrusion is configured to fit snuglyinto the shaped cavity when a distal end of the tubular plunger assemblyabuts the bottom of the vial.
 62. The filter vial kit of claim 60,wherein the shaped cavity has sides that are inclined toward the filterand toward the longitudinal axis.
 63. The filter vial kit of claim 60,wherein the shaped cavity is frusto-conical and centered on thelongitudinal axis and wherein the protrusion is frusto-conical andcentered on the longitudinal axis.
 64. The filter vial kit of claim 60,wherein about the same as a height of the inner sidewall of the annularcap measured along the longitudinal axis.
 65. The filter vial kit ofclaim 60, further comprising a third seal encircling the tubular pistonassembly and located to sealingly engage the vial before the protrusionfits into the shaped cavity during use of the kit.